Considerations of formalin-fixed paraffin-embedded tissue selection and processing for BRCA1/2 tumour testing
| Tissue type | |
| Surgical resection | |
| Core biopsy | At least two core biopsies should be obtained, if possible, and placed in separate cassettes. One tissue core can be dedicated for molecular testing, without being potentially depleted if additional tests such as immunohistochemistry need to be performed. |
| Ischaemic and fixation times Modified from 2019 Pre-analytics for Precision Medicine Project Team of the College of American Pathologists | |
| Cold ischaemic time: <1 hour | Refers to the time, at room temperature, from removal of specimen from the patient to the placement of tissue into formalin. |
| Fixation | |
| Fixative: 10% phosphate-buffered formalin | |
| Minimum fixation time: 6 hours if at room temperature | For specimens placed in formalin and subsequently refrigerated at below 25°C, fixation is slowed and fixation time may need to be adjusted. |
| Maximum fixation time: 24–36 hours for non-fatty tissue at room temperature; 48 hours for tissue with high fat content | |
| Tissue submission for BRCA1/2 testing | |
| Pathologist | |
| Confirms tumour diagnosis. | More than one block may occasionally be needed if tumour is scarce. |
| Chooses a tissue block for testing that has the largest amount of viable tumour, while avoiding/minimising areas of tumour necrosis and inflammation, and avoiding, if possible, selecting multiple small areas of tumour. | The site from which the tumour is chosen, such as ovary or omentum, does not impact BRCA1/2 testing. |
| Orders recut H&E and unstained slides. Marks tumour area(s) on recut H&E for macrodissection or microdissection in the molecular laboratory. Documents percentage viable tumour in marked areas. | |
| Histology laboratory | |
| Cuts one H&E and unstained slides. | Tissue orientation should be same on all the slides, as this will aid the molecular laboratory in successfully identifying the tumour area(s) for dissection. |
| The number of unstained slides and section thickness should follow the local laboratory protocol. | May consist of 5x 10 μm sections or, if tissue is scant, of 10x 5 μm sections. |
| Uses clean technique compatible with downstream molecular testing to cut and package the unstained sections. | Change gloves and replace knife blades between blocks from different patients. Use disposable tools. |